The electronics fabrication industry uses dielectric materials as insulating layers between various circuits and layers of circuits in integrated circuits and related electronic devices. As the electronics fabrication industry moves toward more compact circuitry with finer circuit or line geometry in more densely-packed circuit patterns, the dielectric constant requirements of the insulating layers grows more demanding for lower values.
Therefore, there is a need in the electronic fabrication industry for the replacement of silica-based, interlayer dielectric materials with materials of lower dielectric values. Silica and its modified versions have dielectric values on the order of 3.0 to 5.0 and usually 4.0 to 4.5. Polymeric materials used as replacements for silica as interlayer dielectric materials can have values for dielectric constant in the range of 1.9 to 3.5, which values are highly dependent on the structure of the polymeric materials. To successfully replace silica as an interlayer dielectric material, the properties of polymeric materials must conform to the rigid manufacturing requirements for integrated circuits or microchips in the electronic fabrication industry.
Various polymers have been proposed and utilized as dielectric materials for integrated circuits, wherein such polymeric materials include polyimides and fluorinated poly(arylene ethers).
The presence of fluorine in polymeric dielectric materials was utilized to achieve several results. In the polyimides, fluorine containing substituents lowered the dielectric value, reduced the hydrophilicity, enhanced optical transparency and controlled the solubility of polyimides in organic solvents. The presence of fluorine in the fluorinated poly(arylene ethers) which were proposed as substitutions for low dielectric materials enhanced the synthesis of the fluorinated poly(arylene ethers) by activating the appropriate sites in the polymer precursors as well as providing low dielectric values. In addition, polyimides have been altered with thermally unstable derivatives which decompose to gaseous byproducts to provide a self-foaming polyimide dielectric material which has reduced dielectric constants taking advantage of the low dielectric constant value of air which is 1.00.
Neil Hendricks, Brad Wan and Aaron Smith reported in "Fluorinated Poly(aryl ethers): Low Dielectric Constant, Thermally Stable Polymers for Sub-Half Micron IMD Applications" presented at the DUMIC Conference, Feb. 21-22, 1995, pages 283-289, polymers of fluorinated poly(aryl ethers) developed at Allied Signal provide low dielectric constant, interlayer dielectric materials. These fluorinated poly(aryl ethers) were found to have low dielectric constants and extremely low levels of adsorption and outgassing of moisture during processing. As depicted in FIG. 3 of the article, SiF.sub.4 was detected as a decomposition product of the polymer at temperatures of about 540.degree. C. The polymers were representative of those disclosed in U.S. Pat. No. 5,115,082.
Frank W. Mercer and Timothy D. Goodman reported in "Development of Low Moisture Adsorbing Low Dielectric Constant Dielectrics for Multichip Module Fabrication" in the proceedings of the International Electronics Packaging Conference, Marlborough, Massachusetts, September 1990, pages 1042-1062, that various polyimides can be used as dielectric materials for multichip modules by fluorinating the polymers up to 20% fluorine by weight of the polymer. The incorporation of fluorine-containing groups produce a reduction in dielectric constant and moisture adsorption.
Frank Mercer, David Duff, Janusz Wojtowicz and Timothy Goodman in "Low Dielectric Constant Fluorinated Aryl Ethers Prepared From Decafluorobiphenyl" appearing in Polymer Material Science Engineering, Vol. 66, 1992, pages 198-199, report five new fluorinated poly(aryl ethers). Polymer No. 2 was produced using 9,9-bis(4-hydroxyphenyl)fluorene. The polymers were cited to have good properties for electronic applications.
Frank W. Mercer and Timothy D. Goodman in "Factors Affecting the Moisture Adsorption and Dielectric Constant of Fluorinated Aromatic Polymers" appearing in Polymer Preparation (American Chemical Society Division of Polymer Chemistry), Vol. 32(2), 1991, pages 189-190, disclose that dielectric values of polyimides and fluorinated poly(aryl ethers) are dependent on the presence of polarizable groups such as imide linkages, as well as ketones, sulfones, and nitrile groups. The reported polymers had either these polarizable groups or activated fluorine in their chemical structure. The presence of the polarizable groups was disclosed to have detrimental effects on dielectric constants and moisture adsorption.
Raychem Corporation has patented various fluorinated poly(aryl ethers) which may be crosslinked and/or end capped to control polymer parameters, which polymers are recited to have desirable properties for dielectric materials used in integrated circuit fabrication. These patents include U.S. Pat. Nos. 5,108,840, 5,114,780, 5,145,936, 5,155,175, 5,173,542, 5,204,416, 5,235,044, 5,270,453 and 5,179,188.
L. M. Robeson, A. G. Farnham and J. E. McGrath in "Effect of Structure on the Dynamic Mechanical Behavior of Poly(Aryl Ethers)" appearing in ACS Polymer Preprints, Vol. 16(1), page 476-479, 1975, disclose the synthesis of various poly(aryl ethers), some of which have sulfone bridging groups and other which have oxygen-bridging groups. No particular utility is suggested for these polymers.
L. M. Robeson, A. G. Farnham and J. E. McGrath in "Synthesis and Dynamic Mechanical Characteristics of Poly(Aryl Ethers)" in Applied Polymer Symposium No. 26 1975, pages 373-385, disclose poly(aryl ethers) with sulfone bridging groups. Ether linkages and carbon-to-carbon chemical bonds are also contemplated in replacement of the sulfone bridging unit.
U.S. Pat. No. 3,332,909 discloses polyarylene polyethers having various dihydric dinuclear phenyls wherein R and R' can be hydrocarbon radicals having 1 to 18 carbon atoms, inclusive. The utility of these polymers is recited to be for shaped and molded articles in the preparation of film and fiber products.
M. J. Jurek and J. E. McGrath in "The Synthesis of Poly(Arylene Ethers) via the Ullmann Condensation Reaction" appearing in Polymer Preprint, Vol. 28(11), 1987, pages 180-183, disclose the cuprous catalyst-driven condensation between a halogenated monomer and a dihydric phenyl to produce poly(arylene ethers). The polymers are described as having enhanced radiation stability and lower moisture adsorption relative to polyether sulfones, but no other utility is provided.
The prior art has synthesized various poly(arylene ethers) by the Ullman condensation using cuprous catalysts. These poly(arylene ethers) have not been identified with a particular utility other than as moldable or castable polymers. The prior art has also suggested the use of fluorinated polyimides and fluorinated poly(arylene ethers) produced by different syntheses for use as low dielectric materials in interlayer dielectric materials for integrated circuits and electronic devices. However, these two classes of polymers are not fully acceptable for interlayer dielectric materials due, in the case of polyimides, to the polarizable groups and the hydrophilicity of the materials in the presence of water or high relative humidity, and in the case of fluorinated poly(arylene ethers), the potential evolution of fluorinated byproducts at elevated temperatures and the reactivity of the fluorinated groups, especially with metals. The present invention overcomes these drawbacks by recognizing a unique utility for a class of poly(arylene ethers) as a replacement for silica-based dielectric material wherein the poly(arylene ether) does not have nonaromatic carbons (other than perphenylated carbon), fluorinated substituents or significantly polarizable functional groups, while providing a low dielectric constant, high thermal stability, and low hydrophilicity under high relative humidity conditions, as will be set forth in greater detail below.